Electric elevator or hoisting-machine



(No Model.)

H. HUNTER. ELECTRIC ELEVATOR 0R HOISEING MAOHINE. No. 575,479. Patented Jan. 19, 1897.

"1i 1 1 M- l I na e?) UNITED, STATES PATENT OFFICE.

RUDOLPH M. HUNTER, OF PHILADELPHIA, PENNSYLVANIA.

ELECTRIC ELEVATOR OR HOlSTlNG-MACHINE.

SPECIFICATION forming part of Letters Patent No. 575,479, dated January 19, 1897. Application filed April 5, 1894. Serial No. 506,389. (No modelfl To all whom, it may concern:

Be it known that I, RUDOLPH M. HUNTER, of the city and county of Philadelphia and State of Pennsylvania, have invented an Improvement in Electric Elevators or Hoisting- Machines, of which the following is a specification.

My invention has reference to electric elevators or hoisting-machines; and it consists of certain improvements which are fully set forth in the following specification an d shown in the accompanying drawings, which form a part thereof.

This application (Case No. 271) has particular reference to hoisting apparatus of all kinds operated or controlled by electricity.

lleretofore it has been customary in operating electric elevators or hoisting-machines to operate the winding-drum by means of an electric motor and vary the power or speed of the electric motor by a rheostat or resistance-changer operated directly or indirectly from the cage or a distant place. In systems where dead resistances are required as a means for controlling the current passing to the motor there is a great waste of current in that the current is consumed in heating up the resistances which offer an obstruction to its path. This waste is very material, as elevators and hoisti'ng-machines are frequently stopped and started while in operation for their regular duty.

The object of my invention is to provide a means for controlling the power-motor of an electric elevator from the cage or a distant place, whereby its speed may be varied up to a maximum without the use of dead-resist ances, such as commonly found in rheostats, and this I accomplish by opposing to the current flowing through the power-motor a variable cou nter electromotive force magnetically produced, but independent of that of the power-motor, whereby the current may be checked to any extent desired without material waste.

My improvement therefore com prehends great economy in the operation of electric elevators in addition to the more perfect regulation thereof.

In carrying out my invention I provide the cage with means of any suitable character for raising and lowering it, and these devices I operate with an electric power-motor, preferably of the series type or kind, adapted to the variable duty to which it is subjected in elevator or hoisting work. The electric motor is connected with. the line-circuits leading from the source of supply, and in said circuit I arrange a counterelectromotive-force generator, preferably in the form of a small motor adapted to run free and so controlled that its speed may be readily varied to produce in its revolving element a variable counter elec tromotive force to oppose to the extent desired the initial electromotive force of the line-circuit or source of electric supply. In this manner the current flowing through the large or power motor is varied to a nicety, and both its speed and power is controlled to exactly that which is desired or required. To control the connter-eleetromotive-force generator I provide suitable devices leading to the cage, whereby the said generator may be operated from the cage while the same is in operation or at rest at any position. In addition to the foregoing features I provide means for reversing the currentin thelarge or power motor so as to raise or lower the cage, and also a brake adapted to be automatically thrown into action when the elevator is at rest or when the current is thrown oft the powermotor.

I do not confine myself to the details of construction of the counter-electromotiveforce generator or the means employed for moving the cage or for controlling the said generator from the cage, as all of these may be varied or changed without departing from my invention.

It will be further understood that while my invention is especially adapted to electric elevators it is also applicable to all classes of hoisting machinery, such as lifts and cranes, whether of the stationary or traveling kind. My invention will be better understood by reference to the accompanying drawings, in which- Figure 1 is an elevation of an electric elevator embodying my improvements. Fig. 2 is a diagram illustrating the electric circuits employed in the said elevator. Fig. 3 is a transverse sectional elevation illustrating the counter-electromotive-force generator, and Fig. 4 is a diagram of electric circuits similar in character to Fig. 2, butshowing a modification thereof.

A is the passenger cage or platform, and may move in guides in the elcvator-slnti't, as is customary. The cage is elevated or lowered by means of a cable 13 and a winding drum The cable it passes over a guidesheave b at the top of the shaft. The winding-drum C is combined with an electric motor E through suitable worm and worm wheel or other gearing D. i

F is the motor-circuit leading from the source of electrical energy which may be of any character desired, but preferably of con stant potential.

It is a counter'clectromotive-force generator, and as shown is a type of small shuntmotor having a high-resistance field It in a shunt-circuit '7' about the low-resistance revolvingclementorarmataire. The armature of the counter-clectromotivelorce generator R. is directly in the circuit F and in series with the revolving elemen t of the power-nu)- t'or E.

T is a movable l'rame carrying the brushes t for the generator it, the frame T being provided with teeth with which the teeth on a pivoted segmental rack S mesh, and by which the brushes may be shifted to vary the position of the magnetic poles of the revolving element or armature relative to the poles of the magnetic lield, to the end that the armature speed shall be increased or decreased. The arnntture revolves in suitable bearings and performs no other work than that of its own revolution. Consequel'itly its speed may be raised very high and it may obtain its maximum speed almostinstantly. l3 shifting the brushes the speed may be quickly reduced, and, if desired, thearmatru'e may be brought to rest with rapidity. The resistance of the armature or revolving element of the generator 1 should be such as to be capable ol carnving the maximum current which would be necessary to the power-motor E, but as the power-motoris in active operation when the revolving element of the generator 1% is made to approach a condition of rest it is evident that the cross-section of the wire making up the conductors of the armature might be considerably less than the cross-seetion of the wire upon the power-motor E. It is also evident that as the revolving element of the generator is allowed to rotate freely without doing work, no practical current which would be turned upon it could injure it, since it would respond with so great rapidity that no heating effect could result be fore its counter electromotive t'orce would shut oil the supply of current from theline.

The generator it is an exceedingly small allair ctnnpared with the power-motor E, the only requirements being that it shall be capable 0t carryingthe necessary on rrentlor the motor E, and have cayntcity for a very high velocity. 13y moving the brushes ta most gradual and perfect adjustment of the powermotor E may be had, and the change in the speed of the motor E may be more gradual than is possible with any other method of regulation. The brushes 6 may be carried by an adjustable sleeve, furnished with a pinion T, which pinion meshes with a segmental piv oted rack 8, adapted to be pulled in one di rection by a spring 11 and. be moved in the other direction by a slide .5, having a surface with which pins or rollers I upon a pivoted disk ll. are adzitpted to come in c nt.a .:t. The brushes may be connected with the electric circuits by any flexible electrical eonnectimi, but an excellent manner is to provide the brush-holders with two rings 0, respectively, connected to the two brushes and having sliding contacts as terminals from the circuit 1:, as is clearly indicated in Fig. 3.

In the condition shown in Fig. 1, the lJl'llSlltih' of the generator it are in the position to give the highest speed. to the armature. ll. the disk ll be rotated in either direction, it is evident that after a short movement one or other of the pins or rollers I will come lillOCOliiitHftii with the slide 3 and move the segmental rack: S against the action of the spring 1'. The disk ll is operated by a link K, connecting with a T-shaped crank device .I, which is rocked upon an axis by means of any suitable controlling device leading to the cage A. One form of such controlling device is shown, and consists of two cables I; and hi, one of which, L, connects with the bottom of the cage then passes down around a sheave Z on one arm oi. the device 1, then lmsses upward to a drum 7; on the cage, and adapted to be turned by hand from within the cage, and the other of which cables, M, being connectedv to the top of the cage and. passes up over a sheave in at the top of the shaft, thence downwari'l and around. a sheave on anothe arm of the device J, and thence upward and secured to the same side of the drum 7.: on the cage. It will now be seen that by turning the drum one of the cables ill will be lengthened and the other shortened, causing the nec sary scillation or movement of the devict. ill? the drumv It: is rotated in one direction, the disk it is rotated so that one oi. the pins or rollers 1 comes into action with the slide a, and it the drum 7.: is rotated in the opposite direction, a reverse movement is given to the disk ll and the other pin or roller comes into action. it s evident that any suitalde controlling device extending to the cage oi the elevator for operating the disk ll or the con-- trolling-generator B may be employer'l.

The disk ll. is provided with two contacts I which move over curved eontact-blocl-:s which contact-blocks are connected wil h i he motor-circuits 1* in such a manner thatil' the blocks 1 are moved in one direction the mo tor E is operated to lift the cage, and it moved in the opposite direction the motor is operated to lower the cage. The device g and.

P therefore act as a current-reverscr for the power-motor, in that it reverses the current;

in the armature relatively to the field. As

shown, the reversing-switch completely severs the circuit, through the power-motor E, when the elevator-cage is at rest; but it is evident that, if desired, the circuit may be completed through the contact P, as indicated by the dotted lines W in Fig. 1, if it is desired to keep the generator of counter electromotive force R in continuous operation.

N is a brake-wheel on the motor-shaft, and n is a brake-shoe adapted to be thrown against the brake-wheel. Any movement of the disk II causes the roller Q to ride up out of the notch h in the periphery of the disk, and, through the action of a rod q, move the lever O to withdraw the pressure of the brake-shoe from the brake-wheel. In this manner the brake is automatically applied and removed, being applied when the elevator is at rest and removed when the motor is started up to elevate or lower the cage. The parts are so organized that any movement of the disk H throws off the brake simultaneously or thereabout when closing the circuit F. After this action is performed the operation of the generator R is gradually slowed down, so as to permit more current traversing the powermotor E.

hen the switch G is in the position shown in Fig. 2, the current traverses the revolving elements of both the generator R and the power-motor E in series. If the switch is thrown so as to cover the dotted contacts, then the current will flow through the generator R, over dotted circuit IV, and into the line with the motor E cut out, said circuit corresponding in effect to the circuit shown in dotted lines in Fig. 1.

It is evident that while the field-coils R are shown as in a shunt-circuit 7" around the revolving element of the counter-electronictive-force generator R, the shunt-circuit 7" might not only be shunted relative to revolving element of the counterelectromotiveforce generator but might also be shunted relatively to the power-motor E, as indicated in Fig. 4:. This field B may also have its strength controlled by a suitable resistancechanger R to vary the counter electromotive force. As shown in Fig. 4, the resistance-changer is operated by a bell-crank J, and may be adapted to be moved by anysuitable control device from the cage. By varying the resistance in the field-circuit the counter electromotive force of the generator B may be varied as desired. In Fig. 4 a dotted line shows that instead of the shunt-circuit r being connected to the motor-circuit F beyond the motor E it might be connected upon each side of the revolving element of the generator R, as in Fig. 2.

lVhile I have shown a shunt-motor as a preferable form, it is evident that any other suitable construction of motor may be employed. Forinstance, any series motor adapted to run at high speed might be employed, as such motor would generate a counter electromotive force proportional to its speed and capable of variation by the adjustment of the poles of the revolving element relatively to the poles of the field.

It will be readily understood that it is immaterial to my invention in what manner the poles of the revolving element are adjusted relatively to the poles of the field, for instead of moving the brushes the field-magnets themselves might be moved on. In fact the relative movement between the said poles may be accomplished in any manner desired.

My invention comprehends any means which will control the speed of rotation of the revolving element of the high-speed counterelectromotive-force generator R, whether said variation in speed is controlled mechanically or electrically, the object being to control the counter electromotive force generated in accordance with the requirements irrespective of whether the same is varied by variation in.

the speed of the revolving element, variation in the position of the brushes, variation in the position of the poles of the field relative to those of the revolving element, or varia tion in the relative magnetic induction between the field and the revolving element, as all of these are equivalent means of regulation under my generic invention.

I do not confine myself to any particular construction or details of the apparatus, as the various parts may be modified or changed from that shown, so long as they accomplish the results herein specified, that is to say, controlling the powerunotor of the elevating device by an induced counter electromotive force varying in pressure and produced by magnetic induction.

IVhat I claim as new, and desire to secure by Letters Patent, is

1. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, and an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, with a counterelectromotive-force regulator consisting of electric conductors in series with the motor moving in a magnetic field and provided with flexible means to vary the speed or move ment of the said conductors extending to and controllable from the cage or moving part of the elevator or hoisting apparatus.

2. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, with a counterelectromotive-force regulator consisting of electric conductors in series with the motor moving in a magnetic field and provided with means to vary the speed or movement of the said conductors, and connecting devices extending to the cage or elevating device for ICC controlling the counter electromotive force from a distance.

3. In an electric elevator or hoisting apparatus, the combination of a vertieally-movin g cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, with a counterelectromotive-foree regulator consisting of electric conductors in series with the motor moving in a magnetic field and provided with means to vary the speed or movement of the said conductors, connecting devices extending to the cage or elevating device for controlling the counter electrolnotive force from the said cage, and a reversing-switch to re verse the motor from the cage to reverse the movement thereof.

t. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, with a counter-- electromotive i'orce regulator consisting of electric conductors in series with the motor moving in a magnetic field and provided with means to vary the speed or movement of the said conductors, connecting devices extending to the cage or elevating device for controlling the counter electromotive force from the said cage, a reversing-switch to reverse the motor from the cage to reverse the more ment thereof, at a time when the countercloctromotive-iorce generator has been caused to generate its greatest counter eleetromotive force, and a brake also controlled from the cage for arresting the movement 01 the motor when the cage is at rest and when the con1rter-electromotive-force generator is generating the greatest counter OlOCtl'OlilOtiYO l'orce and adapted to be thrown out ol. action when the cage is moved.

In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, with a counterelectromotive-iforee regulator consisting of electric conductors in series with the motor as an entirety and moving in a magnetic lield, and means extending to a distance to vary the speed of movement of the conductors for producing a dillerence in speed thereof to vary the supply-current to the motor.

(3. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, with a counterelectromotive-1torce regulator consisting of electric conductors in series with the motor moving in a magnetic field and provided with movable brushes to vary the speed of movement of the conductors, and hand-operated devices extending to the cage for shifting the brushes of the counter-elcctromotive-force generator into different positions relatively to the field-poles to vary the current flowing through the po\vermotor.

'7. In an electric elevator or hoisting apparatus, the combination of a vertically-nuning cage or clever-ting device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receive a current from a source of electrical energy, with a counterelectromotive-force generator. consisting of electric conductors in series with the motor moving in a magnetic field and provided with means to vary the speed of movement of the conductors, iieldmagnet coils 01. high resistance to maintain a constant field in. the generator supplied with current independently of the current traversing the moving electric conductors of the generator, areversingswitch to reverse the direction of rotation of the motor, controlling devices extending to the cage for operating the reversing-switeh, and means for timing the several parts whereby the reversing-switch cannot be shifted when the conductors of the conntor-electromotive-iorce generator a re moving slowly and the counter eleetromotive tl'oree generated thereby is low.

8. In an electric elevator or hoisting apparatus, the combination of a vertically-1no\'- ing cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving cnrrentit'roni a source of electrical energy, a counter-clectro motive-force generator consisting of electric conductors in series with the motor and revolving within a magnetic field, means to shift the position of the magnetic poles produced by the revolving electric conductors within the lield, and controlling devices extending to the cage for operating the said pole-shifting devices.

9. In. an electric elevator or hoistingapparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric power-motor mechanically connected to operate the power device and receiving current from a source of electrical energy, a counterelectromotive-force generator to control the operation of the electric motor consisting of a revolving armature operating within a magnetic field and in series with a power-motor, and hand -control devices for varying the speed of the counter electromotive-forcc-regulating armature from the moving cage or elevating device. 1

10. In an electric elevator or hoisting apparatus, the combination of a vertically-nmving cage or elevating device, power devices for raising or lowering the same, an, electric power-motor mechanically connected to operate the power device and receiving current from a source of electrical energy a counterelectromotive-force generator to control the operation of the electric power-motor consisting of a revolving armature operating within a magnetic field and in series with a power-motor, hand-control devices for varying the speed of the eounter-electromotiveforce-regulating armature from the moving cage or elevating devices, and means to reverse the direction of rotation of the motor also operated from the cage or elevating device.

ll. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, a slow-speed power electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, a high-speed generating-motor for generating a counter electromotive force, electric circuits connecting the armatures of the two motors in series, mechanical devices for shifting the magnetic poles of the armature of the highspeed or generating motor relatively to the field-poles thereof to vary the counter electromotive force thereof for the purpose of controlling the current delivered to the slowspecd or power motor, and controlling devices extending to the cage or elevating device for operating the said mechanical devices.

12. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, a slow-speed electric motor mechanically connected to opcrate the power device and receiving current from a source of electrical energy, a counterelectromotive-force-genorating motor having its revolving element electrically connected in series with the revolving element of the power-motor, means to maintain a substantiall y constant magnetic field in the vicinity of the generating-motor irrespective of the counter electromotive force of its revolving element, devices for shifting the poles of said revolving element relatively to the poles of the magnetic field in said last-mentioned or generating motor whereby its counter electromotive force is varied and opposes the initial electromotive force of the operating-cmrent of electricity to vary the speed of the powermotor, and means extending to the cage for operating the pole-shifting devices from the cage to vary the speed of the elevator-cage or elevating device.

13. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, a counter-electromotive-force-generating motor having its revolving element electrically connected in series with the power-motor, means to maintain a substantially constant magnetic field in the vicinity of the generating-motor irrespective of the counter electromotive force of its revolving element, devices for shifting the poles of said revolving element relatively to the poles of the magnetic field in said lastmentioned or generating motor whereby its counter eleetromotive force is varied and opposes the initial electromotive force of the operating-current of electricity to vary the speed of the power-motor, and means extending to the cage for operating the poles, shifting devices from the cage to vary the speed of the elevator, and a current-reversin g switch for the power-motor also controlled from the cage.

14E. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices forraising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, a regulating-generator having its armature connected in series with the power-motor, and flexible means to vary the speed of rotation extending to the cage or elevating device.

15. In an electric elevator, or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the moving the said disk.

16.. The herein-described method of reversing the movement of an electrically-operated elevator which consists in supplying current to an electric powermotor, producing by magnetic induction in the motor-circuit an induced counter electromotive force inclependent of that of the power-motor to control the speed of movement of the said powermotor, gradually increasing the counter electromotive force to cause the power-motor to slow its speed and ultimately to stop, then reversing the current in one of the elements of the power-motor to reverse its rotation, and finally gradually reducing the induced counter electrom'otive force to increase the speed of the power-motor.

17. The herein-described method of reversing the movement of an electrically-operated elevator which consists in supplying currents to a power-motor, producing by a magnetic induction in the motor-circuit an induced counter eleetromotive force independent of that of the power-motor to control the speed of movement ol? the said power-motor, gradually increasing the counter electromotive force to cause the power-motor to slow its speed and ultimately to stop, then reversing the current in one of the elements of the power-motor to reverse its rotation, finally gradually reducing the induced counter electromotive force to increase the speed of the power-motor, and controlling the said operations from the moving cage irrespective of its movement.

18. In an electric elevator or hoisting ap' paratus, the combination of a vertically-mow ing cage or elevating device, power devices for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, a controlling-generator for generating counter electric motive force having a revolving element connected in series with the power-motor and l'noving in a magnetic field, means for shifting the poles of said generator to vary the counter electromotivc .t'orce independent of the action of the power-motor, means extending to the elevator-cage for shifting said poles for the purpose of increasing the speed ol' the counter-electron'iotive-force generator until its counter electromotive force substantially equals the initial electromotive force of the line-current, means for reversing the current in the power-motor when the counter electromotive force of the regulator is at its highest for the purpose of reversing the power-motor, and means extending to the cage for shifting the poles of the counter electromotive force for the purpose of operating the power'motor in the reverse direction.

19. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices [or raising or lowering the same, an electric motor mcclntnieally connected to operate the power device and receiving current from a source of electrical energy, a controlling generator for generating counter electromotive force having a revolving element connected in series with the power-motor and moving in a magnetic field, means for increasing and decreasing the counter electromotive force of said controlling-generator, a reversing-switch for the power-motor, and controlling devices between the moving cage of the elevator and the current-reversing switch, and means [or increasing and decreasing the counter electromotive force of the controlling-generator whereby the counter eleetromotive force is at its maximum when the current in the powermotor is reversed.

20. In an electric elevator or hoisting apparatus, the combination of a vertically-moving cage or elevating device, power devices for raising or lowering the same, an electric motormechanically connected to operate the power device and receiving current from a source of electrical energy, a contrclling-generator for generating counter electrolnolivo force having a revolving element cminected in series with the powm7-nrotor and moving in a magnetic iield, meztns [or increasing and decreasing the counter electromoti ve force of said controll ing-generator, a reversingswil ch "for the power-motor, controlling devices between the moving cage of the elevator and the current-reversing switch, means [or increasing and (lOCl'CiliiSllltf the counter eleetro motive force of the controllinggenerator whereby the counter clectromotive force is at its maximum when the current in the powermotor is reversed, and a mcclu'mical brake acting upon the power-motor tor the purpose of arresting its rotation when the counter electromotive force is at its maximum.

21.. In an electric elevator or lmisting apparatus, the comlgiination of a vtn-tically-moving cage or elevating device, power devices for raising or lowering the same, an electric motormechanically connected to operate the power device and. receiving current from a source of electrical energy, a controlliug-generator for generating counter eleetrmnotive force havinga revolving element connected in series with the power-motor and moving in a magnetic field, means for increasing and dc;- (fl U.

said controlling generator, a reversing for the power-motor, controlling devices between the moving cage of the elevator and the current-reversing switch, means for increasing and decreasing the counter electromotive force ot the controllinggenerator whereby the counter clcctromotive force is at its maximum when the current in the powermotor is reversed, and. means for interrupting the current in the power-motor in the act of reversing it when the counter OlOCt-IOIUOtlVO force is at its highest.

In an electric elevator or hoisting ap paratus, the combination of a vertically-uloving cage or elevating device power devices for raising or lowering the same, an electric motor mechanically coi'niected to operate the power device and receiving current from a source of electrical energy, a, controlling-generator for: generating counter electromotive force having a revolving clement co] 1 1 rec ted in series with the power-motor and moving in a magnetic iicld, means for varying the counter eleetromotive force of the controlling-gencrator, a switch for cutting the power-motor out of circuit, and connecting devices extmuling to the moving cage or elevating device whereby the electric circuit to the power-motor is broken when the counter OlO(3iil.'Ol1l(')tl\'(, force is at its maximum.

23. In an electric elevator or hoisting apparatus, the combination of a vertically-mcv' ing cage or elevating device, power dev for raising or lowering the same, an electric motor mechanically connected to operate the power device and receiving current from a source of electrical energy, a controllinggem erator for generating counter electromotive force having a revolving element connected in series with the power-motor and moving in a magnetic field, means for varying the counter eleetromotive force of the controlling-generator, a switch for cutting the power-motor out of circuit, connecting devices extending to the moving cage or elevating device whereby the electric circuit to the power-motor is broken when the counter electromotive force is at its maximum, and means to reverse the current in the power -1notor prior to changing the counter electromotive force of the controlling-generator.

24c. The herein-described method of operatin g electric hoisting or elevating machines, 

